1. Field of the Invention
The present invention relates to an absorbent article for use in disposable diapers, protectors against incontinence or sanitary napkins; more specifically, the present invention relates to a super absorbent article of a slim type.
2. Prior Art
In disposable diapers and sanitary napkins, an absorption core to absorb urine and blood of menstruation is interposed between the back sheet comprising a liquid non-permeable resin sheet and an inner top sheet in direct contact to the skin of a wearer. Between the upper sheet and lower sheet comprising thin papers in the absorbent core is interposed a mixture of ground pulp and super absorbent polymers (abbreviated as "SAP" hereinafter) such as polyacrylic acid salts or is interposed SAP singly. Because SAP have higher absorptivity than that of pulp, such absorption core interposed with SAP exerts more excellent absorptivity of urine and blood of menstruation, compared with an absorption core interposed only with pulp, so that the resulting absorption core can be prepared of a slim type. Additionally, SAP are powdery at its dry state; once SAP absorb urine and blood of menstruation, however, SAP swell and is then solidified in the form of gel. Therefore, absorbed urine or blood of menstruation can be retained securely in the absorption core, which can prevent the reversion or outward oozing of the absorbed urine and blood of menstruation. Additionally because SAP are softer even at its dry state and swelling state (in the form of gel) than pulp, the absorption core using SAP are so softer than an absorption core using only pulp that the absorption core can readily deform along the body of a wearer, which presents comfortable feeling on wearing.
When the amount of SAP is increased in the absorption core so as to elevate the absorptivity, the SAP powder at its dry state prior to absorption shifts in the absorption core following the motion of a wearer, with the resulting variation in the SAP distribution. When urine or blood of menstruation is spotted at a part with a lower content of SAP, then, the urine or blood of menstruation cannot be absorbed into the smaller amount of SAP, with the resulting deterioration of the absorptivity. After absorption, furthermore, the SAP gel may shift to be solidified in the absorption core or the resulting mass might tear or break the upper sheet and lower sheet, disadvantageously, which presents unpleasant feeling to a wearer.
So as to overcome the problems described above, for example, Japanese Patent Publication No.61-30041, Japanese Patent Provisional No. 6-254118, and Japanese Patent Publication No.7-73591 and furthermore Japanese Utility Model Publication No.63-23078 describe an invention or a utility model, relating to an absorption core produced by dispersing a given amount of a super absorbent material at an interval on the whole surface of a sheet, covering a cover sheet with a great number of recesses formed thereon over the sheet, and bonding the cover sheet to the sheet.
In such manner, the super absorbent material is pressed against a part to be placed, by uniformly distributing a given amount of a super absorbent material over the whole absorption core and covering such cover sheet over the absorption core. Hence, the shift of the super absorbent material in the absorption core can be prevented, while the whole thickness of the absorption core can be uniformly retained and the absorptivity can be enhanced.
In the absorption core as described above, the depth and diameter of each of the recesses on the cover sheet should be sufficiently enlarged so as not to prevent the swelling of the super absorbent material, so that the volume of the space inside each of the recesses should be larger than the volume of the given amount of the super absorbent material. Therefore, the dimension of the thickness of the absorption core is so large, which limits the preparation of an absorbent article of a slim type. When the space in each of the recesses on the cover sheet is made small so as to prepare an absorption core of a slim type, the swelling of the super absorbent material is prevented when the core absorbs urine or blood of menstruation, which reduces the absorptivity.
Furthermore, when covering a cover sheet over the absorption core, the cover sheet should cover a sheet mounting the super absorbent material, so that the super absorbent material is to be placed just in the recesses formed on the cover sheet. Then, the cover sheet should be bonded to the sheet mounting the super absorbent material at a part between individual recesses on the cover sheet. Accordingly, the bonding lines on which the cover sheet is bonded to the sheet mounting the super absorbent material are so complex that the bonding work of both the sheets is laborious.
The present invention can overcome the aforementioned problems of prior art and provides an absorbent article capable of preventing the shift of the absorbent material in the absorption core and dispersing uniformly the absorbent material over the whole absorption core without exception and secururing a zone where the absorption material after absorption can swell.
It is another object of the present invention to provide an absorbent article of a slim type, which can absolutely prevent the outward pouring of the absorbent material and can be produced readily.